@djMax, I found Paypal reader here , The reader looks cool, I guess it is OEM/Repackage of square credit reader.

The square reader is reverse engineer the iphone audio interface as well as iOS which would be a little a bit pain in the butt to use, the speed of swip and make sure insert it properly, and it only support one track of card.

In the other side We Arduino is able to connect the magnetic card reader/writer to read or write all 3 tracks of card, meanwhile Arduino support PayPass reader to read/write PayPass contact-less credit card, and it support contact reader to support ISO/IEC 7810 interface contact credit card.

All above of reader/writers could have bank industry certification. The writing function is in theory only, the reason is obviously.

there's no point in using a card reader when they can just click a paypal button and type in their cc info or log into their paypal account. The transactions are, at most frequent, once a week.

You might be missing the point "card in present" v.s. "card not present", by your idea , say "card in present" rate is 1.5%, every 10k credit card transaction will save you 200 USD. It is your idea and your money.

card in present rate is less than card not present for sure, rate is changed by different merchant product, for "online medicine" as example, the card not present could be over 10% since it is high risk product. Same time card in present rate for restaurant some time could far less than other industry rate. "card present: 1.5%" is I make up, we need to wait djMax give us correct rate.